The present invention relates to a method and apparatus for stirring fluids and undergoing combustion and fluid undergoing convective heat transfer with rotational energy.
Prior art burner systems rely upon the momentum of the injected combustion air to produce a turbulating effect in the combustion volume. Since the mechanical efficiency of momentum exchange of the injected combustion air and surrounding combustion gases is low, the effective turbulation of conventional combustion systems is minimal. Such turbulation is also dependent upon the combustion air flow rate into the system and on the pressure differential which exists across the entire heating system.
An object of the present invention is to provide energetic stirring and mixing within a combustion volume, completely independent of the combustion air flow rate and the pressure drop associated with other flow components of the system.
The present invention also relates to improving energy recovery in existing heating and gas recovery systems and to improved recovery of the major share of the sensible and latent heat energy in the combustion products in a burner-heat exchanger for carbonaceous fuels. Prior art boilers, furnaces and water heaters which are used in residential and commercial heating installations with the available liquid, solid, and gaseous fuels tend to be thermodynamically inefficient for many reasons. Under optimum steady state operating conditions, it is necessary for these heating systems to reject at least 15% of the fuel energy in discharging combustion products as sensible and latent heat. Since it is not economic to fabricate these heating systems from corrosion-resistant materials of construction, it is imperative that the temperature level of the discharging fuel gases remain above the dew point of the condensible portion of the discharge; in other words, condensation of flue products within existing heat exchanger systems must be avoided in order to minimize corrosion problems.
An object of the present invention is to provide an economizer of simplified construction which may be economically fabricated from corrosion-resistant materials and which is readily adapted to existing heating systems to permit recovery of the energy which is normally rejected as sensible energy and latent heat energy in the discharging flue products. A further object of the present invention is to provide an economizer which enables existing heating systems to operate in a conventional manner, discharging flue products at elevated temperatures necessary to avoid condensation but wherein the energy in the discharged products is recovered to achieve high thermodynamic efficiency.
Prior art combustion and heat exchanger flue systems have widely varying flow characteristics which result in resonant coupling or instability in operation. Another object of the present invention is to provide a dynamic flue system which is completely stable and obviates existing flue difficulties.
Prior art heating systems require the use of "draft-diverter" components which interconnect the heating systems with conventional flue systems. Under adverse draft conditions resulting in unstable operation of the heating systems, it is well known that toxic gases may be emitted into living quarters through the draft diverter components. A further object of the present invention is to provide positive venting means for flue products to allow safe operation of existing heating systems under all conditions.
It is well known that very compact and efficient gas generator systems can be devised in which direct contact heat transfer occurs between combustion products and injected water. However, these systems have not found commercial acceptance due to corrosion problems and difficulty in recovering heat from the humid combustion products. Still another object of the present invention is to allow the use of simplified gas generating systems which provide direct contact heat transfer.
Another object of the present invention is to provide induction means for combustion air whereby gases are discharged from the system after they have undergone complete heat transfer and after the condensible portion of the flue products is removed, thereby substantially reducing the accessory power requirements of such a system.
Prior art heating systems, particularly the so-called "higher performance" systems, are plagued by the difficulty of matching the combustion device with conventional heat exchangers. This difficulty has prevented convenient retrofitting of heating systems in the field to accommodate improved combustion components. Another object of the present invention is to provide a high performance retrofit capability for all existing heating systems which are gas, oil, or solid fuel fired.
Prior art heating systems, particularly those which are fired with liquid fuels and fuel atomizing devices of the conventional nozzle type, have serious difficulty in providing modulated firing rates, particularly at low firing rates when the draft conditions of conventional heating systems are marginal. Another object of the present invention is to provide modulated firing rate capability under extremely low firing rate conditions with means for positive venting of flue products.
An object of the present invention is to provide an economical and efficient automatic draft control system. This system permits a universal interface of the invention, when used to recover waste heat from flue gases, to any existing heating or other combustion device, including those operating in the atmospheric mode. Automatic control means responsive to the deviation between a predetermined parameter and the actual operating condition of that parameter are provided in order to commonly or independently control the rate at which combustion products are discharged by the primary device and induced to the heat exchanger of the invention and control the ratio of fuel to air in the combustion device. In this manner, it is possible to obtain optimum combustion by maintaining a predetermined ratio between air and fuel. This draft control system is operable over a wide range of fixed firing rates or at variable firing rates.
Prior art heating systems are restricted to using fuels having a low sulfur content primarily due to the corrosion problem which is encountered with these fuels. Another object of the present invention is to permit the use of lower grade fuels which generate products normally considered prohibitive for conventional heat exchangers.
It is well known that the temperature of the flame zone is an important consideration from the standpoints of burner control and possible elimination of pollutant emissions. Prior art heating systems have relatively poor regulation of flame temperature due to inadequate convective heat transfer from the combustion zone with the available stirring energy and critical dependence of this stirring energy upon the flow of combustion air. A further object of the present invention is to provide means for positively controlling the flame temperature within the combustion zone to maximize volumetric firing rate and minimize generation of pollutant emissions.
Prior art combustion systems have difficulty, particularly in the combustion of fuels derived from coal, in disposing of the inert and ash content of the fueld residue without clogging the system. A still further object of the present invention is to: (1) remove the generated ash from the combustion products or fixated fuel gases at a temperature which is below the fusion point for the ash content; and (2) eliminate restrictive flow passages where solids may collect and clog.
Prior art combustion systems have difficulty in staging the admission of combustion air within the combustion process in order to optimize the generation and fixation of fuel gases within the primary zone of the burner and completely after-burning these gases in the later stages of the burner. Another object of this invention is to optimize the staging of the oxidation process for a variety of fuels.
Still another object of the present invention is to provide, for a burner, a mechanical stirrer which has self-cooling and self-lubricating features and which is extremely lightweight and dynamically balanced.
Existing combusion systems rely completely upon the momentum exchange from the injected combustion air for mixing of the combustion chamber gases and recirculating of the combustion products for stable operation. Under optimum experimental conditions, the maximum mechanical efficiency of such a "jet-pump" system is less than 7%. In other words, less than 7% of the kinetic energy available in the injected combustion air is available for turbulating the combustion chamber and providing the necessary mixing energy. This is a serious limitation in prior art burner practice, although it is well known that the stability of a combustion process and its volumetric firing rate potential and heat transfer effectiveness are all parameters which are directly proportional to the available mixing energy of the system. It must also be noted that the blower elements and blower housings which are used with conventional oil burners involve substantial diffuser losses and a limited range of stable operation. Conduction of the combustion air to the combustion chamber is also accompanied by total pressure losses, so that the mechanical efficiency of the blower in a conventional oil burner system is always less than 60%. The energy which is actually available for mixing and turbulating the conventional burner system is therefore the product of the air blower and "jet-mix" efficiencies, less than 0.60.times.0.07, or 4.2%. It is an object of the present invention to provide a burner which increases the mixing energy available inside the combustion chamber by a factor of ten times that available in conventional burners.
It is a further object of the present invention to provide a basic structure which, with slight modification, can serve as a highly efficient burner, a highly efficient heat exchanger or a highly efficient economizer for use in combination with an existing heating system to improve its efficiency.
For fuels containing sulfur, the formation of sulfuric acid is inherent in a combustion device. A serious disadvantage of prior art combustion devices resides in the use of restricted flow passages where sulfuric acid may collect and cause corrosion. Conventionally, in larger utility boilers, the corroding material is blown out by shutting down the boiler and using steam to clean the passages. An object of the present invention is to minimize corrosion by eliminating constrictive passages and by continuously flowing water and steam through the system as part of the combustion process to clean out the corrosive materials and reduce the amount of corrosive materials which are produced.